The Jackson family are suing the promoter for its alleged role in Michael's 2009 death, with Katherine accusing AEG of being negligent by hiring Dr Conrad Murray, who was jailed for the involuntary manslaughter of Michael.

Osbourne's involvement comes after she revealed on her CBS show The Talk that AEG executives told her Michael wasn't well enough to perform during rehearsals for his scheduled shows at the O2 Arena in London.

"There were certain people that work at that company that knew Michael Jackson was not well and they didn't care because it's business," she said.

"Whether he performed, or he didn't, they would still make money. I've had conversations with certain people at that company [AEG] who have said exactly that to me.

"If they [the Jackson family] would like me to go to court, I will stand up and tell them who said that to me."

A source has since told Radar Online: "Sharon Osbourne was added to the plaintiff's witness list. The jury will be extremely interested to hear what Sharon has to say.

"Sharon is extremely credible and she doesn't have an axe to grind with anyone in this case. She just wants to tell the truth about what certain key executives at AEG told her before Michael tragically passed away.

"This goes to the heart of Katherine's case that AEG knew Michael wasn't healthy and everyone at AEG knew it."

Jury selection in the lawsuit began on Tuesday (April 2) in Los Angeles. The trial is expected to last up to three months.